Pre-Algebra : Circumference of a Circle

Example Questions

Example Question #1 : Circumference Of A Circle

Becky's house is surrounded by a circular lake that Becky runs around each day. If Becky wants to figure out the distance she runs around the lake, what formula should Becky use?

Explanation:

Becky should use the circumfrence formula to find the distance she runs of a lake.

Example Question #1 : Circumference Of A Circle

What is the circumference of a circle with an area equal to ?

Explanation:

Using the area, solve for the radius:

Divide by :

Take the square root:

Plug this radius into the formula for the circumference:

Example Question #2 : Perimeter

What is the circumference of a circle with a radius equal to ?

Explanation:

The circumference can be solved using the following equation:

Example Question #1 : Circumference Of A Circle

What is the circumference of a circle with a radius of ?

Explanation:

The circumference can be solved using the following equation:

Where  represents the radius. Therefore, when we substitute our radius in we get:

Example Question #1 : Circumference Of A Circle

The perimeter of a given rectangle is equal to the circumference of a given circle. The circle has radius  inches; the width of the rectangle is  inches. What is the length of the rectangle?

inches

inches

inches

inches

inches

inches

Explanation:

The circumference of a circle with radius  inches is

inches.

The perimeter of the rectangle is therefore  inches. To find its length, substitute  and  into the equation and solve for :

inches

Example Question #2 : Circumference Of A Circle

Determine the circumference of the circle if the radius is 20.

Explanation:

Write the formula for circumference.

Example Question #1 : Circumference Of A Circle

Given the area of the circle is , what is the circumference of the circle?

Explanation:

Write the formula for the area of a circle.

Substitute the area.

Write the circumference of the circle.

Example Question #1 : Perimeter

Find the circumference of a circle with an area of .

Explanation:

Write the area formula in order to find the radius.

Substitute the area.

Write the circumference formula.

Example Question #3 : Circumference Of A Circle

Determine the circumference of the circle if the radius is .

Explanation:

Write the formula for the circumference of a circle.

Substitute the radius into the formula.

Example Question #1 : Circumference Of A Circle

Find the circumference of a circle with a radius of .